Amorphous (As₃₀Sb₁₅Se₅₅)_100−xTe_x (with 0 ≤ x ≤ 12.5 at.%) were prepared by thermal evaporation. The optical transmission and reflection spectra of these films were measured in the wavelength range of 400–900 nm. The mechanism of the optical absorption follows the rule of allowed non-direct transition. It was found that, the optical band gab E₀ decreases while the width of localized states (Urbach energy) E_c increases by increasing Te content. The relationship between E₀ and chemical composition of the (As₃₀Sb₁₅Se₅₅)_100−xTe_x system were discussed in terms of Cohesive energy (CE), the average heat of atomization H_s, and the average coordination number N_r. The later are computed from the heat of atomization and the coordination number of used elements, respectively.